Frequently, in the optics industry, there is a need for custom beam splitters, which can split a given wavelength into sub-beams at given percentages, e.g. a 30%/70% reflective/transmissive beam splitter for 532 nm light. A custom beam splitter can cost $3,000 for a very simple flat plate beam splitter up to $12,000 for more complex cube beam splitters. Unfortunately, the conventional custom beam splitters are only designed one splitting percentage and a small range of wavelengths.
U.S. Pat. No. 6,084,717 issued Jul. 4, 2000 to Wood et al, discloses a laser beam splitter, in which plate beam splitters, designed for a specific wavelength and a specific splitting ratio, are used to divide an input beam into eight equal output beams by passing sub-beams in sequence through the plate beam splitters to obtain the desired output ratio.
Similarly, U.S. Pat. No. 5,798,867 issued Aug. 25, 1998 to Uchida et al, discloses a laser beam splitter, in which a beam splitter plate with a coating that varies along its length, is laterally adjustable to adjust the beam splitting ratio. Again, the coating is designed for a certain wavelength of input light and a certain angle of incidence.
U.S. Pat. No. 6,678,447 relates to a polarization beam splitter, which requires a plurality of modules that have to be added, rotated and removed, as varying splitting ratios are required. Furthermore the location of the output port is constantly changing as the modules are rotated and removed.
Another polarization beam splitter is disclosed in U.S. Pat. No 4,859,029 issued Aug. 22, 1989 to Durrell, requiring a high angle of incidence and polarized light.
An object of the present invention is to overcome the shortcomings of the prior art by providing a simple beam splitter that can be adjusted to give any reflectivity between about 10% and about 100% and a tranmsission that varies from about 0% to about 90% for any wavelength in the region of interest, e.g. visible, IR etc.
Another object of the present invention is to provide a variable beamsplitter in which the input and output port positions are constant for all beamsplitting ratios.